(1) Field of the Invention
The present invention relates to a broadcasting apparatus for broadcasting a data carousel, a receiving apparatus for receiving the data carousel, and a method and an apparatus for caching contents that are synchronized with broadcast programs or commercials.
(2) Description of Related Art
Digital broadcast programs include ordinary broadcast programs such as movies or dramas, and data broadcast programs. Ordinary broadcast programs are mainly composed of video streams and audio streams. Receiving apparatuses reproduces the ordinary broadcast programs the instant they receive them. The data broadcast programs achieve a pseudo interactive operation with viewers by repeatedly transmitting broadcast program data at intervals of 5 seconds, for example.
A method of repeatedly transmitting contents of data broadcast programs is called data carousel method. An international standard defines a DSM-CC data carousel method (hereinafter referred to as carousel method), where DSM-CC stands for Digital Storage Media Command and Control. For detailed information, refer to the standard: ISO/IEC 13818-6 “Information Technology—Generic Coding of Moving Pictures and Associated Audio—Part 6: Extensions for DSM-CC”. Japanese BS digital broadcasting has also adopted the carousel method as a method of transmitting multimedia data broadcasts. For detailed information, refer to the standard ARIB STD-B24: “Data Broadcast Encoding and Transmission for Digital Broadcasting” by the Association of Radio Industries and Businesses.
In reproducing a data broadcast program, a receiving apparatus interactively selects, receives, and reproduces a content in accordance with user instructions. In this case, after a viewer selects a content while another content is reproduced and displayed on the screen, the user must wait one cycle of the responding transmission at the maximum until the selected content is displayed. A technique for reducing the wait time is disclosed in Japanese Laid-Open Patent Application No. 10-126753 “Terminal apparatus that performs, using cache, high-speed display of operator-selected video data among great amount of video data broadcast in one way, and method for use in the terminal apparatus”. This technique allows a user-selected content to be immediately reproduced and displayed by caching into a memory a content having a high possibility of being displayed next to the currently displayed content.
The above technique has a problem, however, that immediately after a data broadcast program begins, the broadcast data for the program has not been cached at all. This causes a problem that immediately after a data broadcast program begins, the user must wait for some time until a response for an interactive operation is displayed.